In general, heating apparatuses include heat exchangers in which heat is exchanged between combustion products and heat media (heating water) by combustion of fuel to perform heating by using the heated heat media or supply hot water.
In the fin-tube type heat exchanger according to the related art, a tube in which a heat medium flows along an inner space thereof is coupled to a heat transfer fin protruding from a surface of the tube.
Referring to FIGS. 1 and 2, in the fin-tube type heat exchanger 1 according to the related art, a plurality of heat transfer fins 20 are parallely coupled to be spaced a predetermined distance from each other on outer surfaces of a plurality of tubes 10 each of which has a rectangular section, and a plurality of insertion holes 21 each of which has a shape corresponding to that of each of the tubes 10 are defined in the heat transfer fins 20 to allow the tubes 10 to be inserted therein. Here, portions where the outer surfaces of the tubes 10 contact the insertion holes 21 are welded and coupled to each other. End plates 30 and 40 are respectively bonded and connected to both ends of the tubes 10 to which the heat transfer fins 20 are coupled. Also, a plurality of insertion holes 31 and 41 each of which has a shape corresponding to that of each of the tubes 10 are defined in the end plates 30 and 40 to allow both ends of the tubes 10 to be inserted therein and then to be welded and coupled thereto. Flow path caps 50 (51, 52, and 53) are coupled to a front side of the end plate 30, and flow path caps 60 (61 and 62) are coupled to a rear side of the end plate 40, and thus a flow path of the heat medium flowing inside the tubes 10 is switched. Also, an inlet 51a and outlet 53a of the heat medium are disposed on the flow path caps 51 and 53, respectively.
Since such a fin-tube type heat exchanger has high heat-exchanging efficiency when compared to different types of heat exchangers and a simple structure, the fin-tube type heat exchanger may be manufactured in a compact size. Also, since the fin-tube type heat exchanger has high mass productivity, the fin-tube type heat exchanger is being widely utilized for domestic and industrial uses such as a boiler and air conditioner. Also, since the fin-tube type heat exchanger has a small size and secures a wide heat transfer area, the fin-tube type heat exchanger has excellent heat efficiency when compared to a heat exchanger to which a Hi-fin or corrugated tube is applied.
However, in the fin-tube type heat exchanger according to the related art, as illustrated in FIG. 3, a lower end 10a of the tube 10 disposed at a side into which the combustion product generated by the combustion of a burner 70 is introduced may be locally overheated to generate bubbles B in the heat medium passing inside the tube 10, thereby causing boiling noises. Also, foreign substances such as calcium contained in the heat medium adheres to an area on which the flow inside the tube 10 is delayed to significantly deteriorate efficiency of the heat exchanger. In a severe case, the area to which the foreign substances adhere may be damaged due to the overheating.
There are prior arts for solving the above-described limitations, that is, a boiling prevention member of a heat exchanger in which a plurality of blades tilted at a predetermined angle are inserted to switch a flow path of heating water in a tube (heating tube) is disclosed in Korean Utility Publication Gazette No. 20-1998-047520, and a tube (heating tube) having spiral grooves defined in a predetermined section on an inner surface of the tube so that heating water rotates to be mixed while passing through the spiral grooves is disclosed in Korean Utility Publication Gazette No. 20-1998-047521. However, these prior arts are applicable to a case in which the tube has a circular section. Thus, when a rectangular tube having a relatively large heat transfer area to a unit through area is used instead of the circular tube so as to develop a compact heat exchanger having high efficiency by further increasing heat-exchange efficiency, since the boiling prevention member or the spiral grooves disclosed in the prior art documents are not easily adopted inside the tube having a high rectangle ratio, the related art are not applicable.
Referring to FIG. 4, in the fin-tube type heat exchanger according to the related art, each of the heat transfer fins 20 has a flat plate shape, and the combustion product linearly passes between the heat transfer fins 20 parallely disposed adjacent to each other. In this case, as illustrated in FIG. 5, a temperature at a portion on which the combustion product contacts the heat transfer fin 20 is maintained at a temperature T∞ over a predetermined section A from a start end of the heat transfer fin 20 to which the combustion product is introduced, and then the combustion product changes to a temperature T0. Here, a point at which the combustion product starts at the temperature T0 may be called a temperature boundary layer formation point B. After the temperature boundary layer formation point B, a portion at which the combustion product contacts the heat transfer fin 20 becomes to a temperature T0, as the combustion product is away from the heat transfer fin 20, the fluid increases up to the temperature T∞.
In this case, a point at which the combustion product has a relatively low temperature is expressed by an oblique line in FIG. 5. Thus, when the heat transfer fin 20 is processed in a flat plate shape, the heat exchange efficiency decreases on an area after the temperature boundary layer formation point B. Also, when the heat transfer fins 20 are disposed with a narrow distance ace therebetween so that the temperature boundary layer formation point B is far away from the start end of the heat transfer fin 20, the combustion product increases in flow resistance to deteriorate the heat efficiency.